Blow molding is a fabrication method for hollow thermoplastic shapes. There are two general classes of plastic products made using the blow-molding process and related machinery: packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and other containers. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like. The term “articles” is used to encompass either or both packaging products and technical parts.
The blow-molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a thermoplastic parison is lowered from an extruder and between mold halves. The mold halves close around the parison, and the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow-molding process.
In intermittent extrusion, the molds are mounted to a common platen and the parisons are extruded by either a reciprocating screw extruder or by a ram accumulator which holds in readiness a volume of molten plastic material needed to make the next article or articles. In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment of the parison is severed and positioned into a mold. The molds can be moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action. When the parison is extruded, the mold is moved under the extruder die or flow head to receive the parison segment and then is moved to a blowing station.
The positioning of the parison relative to the mold in a rotary system is relatively difficult. Therefore, many of the current blow-molding machines use the reciprocating mold concept according to which the molds are shuttled back and forth from station to station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate.
A. Horizontal Rotary Blow-Molding Machines
Horizontal rotary blow-molding machines allow for high production rates of uniform containers. Such machines index circumferentially spaced mold halves in steps around a vertical axis. The mold halves each capture a vertical, continuously growing parison at an extrusion station. In one machine, the flow head extruding the parison moves up away from the mold halves after the mold halves close to capture the parison. The parison is severed adjacent the top of the mold halves, the mold halves are moved away from the extrusion station, and a top blow pin is moved into the end of the captured parison at the top of the mold halves to seal the mold cavity and blow the parison. Subsequently, the flow head and dependent parison are lowered back to the initial position so that the new parison is in position to be captured by the next pair of mold halves. The blown parison cools as the mold halves are rotated around the machine, following which the mold halves open at an ejection station and the finished article, commonly a bottle or other article, is ejected from between the mold halves. The machine includes an in-mold labeling station between the ejection station and the extrusion station for applying labels to the interior surfaces of the mold cavities.
In another horizontal rotary blow-molding machine the parison grows down over a blow pin at the bottom of the mold halves before closing of the mold halves. The flow head is moved up above the closed mold before severing of the new parison from the captured parison. The mold is then indexed laterally to the next station without dropping and the captured parison is blown within the cavity. In a further horizontal rotary blow-molding machine, the whole turntable supporting all of the mold halves is raised and lowered during rotation as each mold captures a parison at the extrusion station.
B. Labeling Machinery
Conventionally, labels are supplied to mold sections of rotary blow-molding machines by an in-mold labeling apparatus having transfer heads that engage and move the labels. The transfer heads are connected to a drive mechanism that cycles the heads back and forth between a label pick up position and a label transfer position. The heads carry vacuum cups for engaging and holding labels. When in the label pick up position, the heads are moved against labels held in label magazines to form vacuum connections with the labels. Movement of the heads away from the magazines pulls labels from the magazines. The labels are carried with the heads for subsequent placement in cavities in the mold sections.
During the cycle of a conventional in-mold labeling apparatus, it is necessary to move the vacuum cups on the transfer heads into engagement with the lead label in the magazine and form a strong vacuum connection with the label sufficient to assure that the label is held in place on the head as the head is withdrawn from the magazine and the label is stripped out past the gripping fingers in the magazine. The head is dwelled or paused for a relatively long interval with the cup on the label in order to assure that the pressure within the cup is reduced sufficiently to form the desired strong vacuum connection with the label. The dwell interval is required to assure that the air captured within the cup upon physical engagement with the label can be withdrawn from the cup through the vacuum manifold to the vacuum source thereby reducing the pressure in the cup and forming the desired strong connection.
It is conventional to minimize the dwell interval during which the connection is formed by reducing the vacuum of the vacuum source and by locating the vacuum source close to the suction cup. The labels cannot be reliably removed from the magazines, however, if the interval is made too small or the vacuum is too weak.
Single labels cannot be withdrawn using a very strong vacuum. This problem occurs because, if the vacuum is too high, air is drawn through the thickness of the lead label and the cup holds two or more labels in place and will withdraw all the held labels when moved from the label magazine. Withdrawal of more than one label at a time produces at least a reject article and can result in shut down of an entire blow-molding line.
The baskets used to supply labels for pick up by in-mold label apparatus extend away from the label pick up positions. As labels are exhausted from the fronts of the baskets, operators must refill the baskets in order to assure continued in-mold labeling. The baskets are located close to the other parts of the in-mold labeling apparatus and the blow-molding machine. This close proximity makes loading of the baskets difficult.
The label baskets are mounted on the frame of the in-mold labeling system using a connection which permits limited rotation of the baskets to adjust the rotary positions of the labels as presented to the pick up heads. This rotational adjustment of the baskets permits limited adjustment of the angular position of the labels when picked up from the basket and when placed in the mold sections. In some blow-molding operations, labels are placed in mold cavities which are angularly oriented relative to the label transfer heads. The limited rotational adjustability of the magazines is not sufficient to permit labels to be rotated through a relatively large angle for proper placement in these oriented mold cavities. Mounting of the magazines at a rotational position sufficient to assure proper orientation for placement of the labels in the angularly oriented mold sections can make it difficult to refill the baskets with labels in order to assure continuous operation of the blow molding line.
U.S. Pat. No. 4,840,366 discloses an in-mold labeling apparatus and method in which a label transfer assembly is moved up and down between label pick up and label transfer or discharge positions by rotation of a fly wheel carrying a cam follower. The cam follower is fitted in a cam slot in a transverse cam member mounted on the label transport assembly. The transport assembly includes a pair of label carriages. When the assembly is at the lower or label pick up position, stops collapse the carriages to extend and retract the label transfer heads and vacuum cups for label pick up in response to the vertical movement of the assembly. Likewise, when the rotation of the drive member elevates the label transfer assembly to the upper or transfer position, stops collapse the carriages to extend the heads, vacuum cups, and held labels for movement of the labels into mold cavities and transfer of labels to the mold halves. Vertical movement of the label transfer assembly and the extension and retraction of the label transfer heads are both driven through the single connection between the rotating drive member and the cam plate.
Current rotary blow-molding machines are capable of operating at high production rates. In order to operate these machines at maximum speed, the in-mold labeling apparatus must necessarily operate rapidly with great reliability and a short cycle time. Increased production rates for blow molding articles requires that the in-mold labeling apparatus must pick up and place labels in the mold halves at ever-increasing rates. In an in-mold labeling apparatus such as the apparatus disclosed in U.S. Pat. No. 4,840,366 where the head assemblies move reciprocally, increased production rates greatly increase inertial forces on moving parts and cause vibration and undesired stressing in the entire machine. The vibration and stresses extend from the in-mold labeling apparatus down through the drive connection to the common drive motor used to power the apparatus and also the blow-molding machine.
The unwanted forces occur because of the large loading forces required to rapidly accelerate and decelerate the relatively large members of the in-mold labeling apparatus up and down between the labeling pick up positions and because of the large forces required to rapidly accelerate and decelerate the label transfer heads as they are moved in and out during label pick up and label transfer. Wear is experienced at the cam plate where the drive member transmits the forces necessary to both reciprocate the label transfer assembly between the pick up and labeling positions and extend and retract the label transfer heads.
U.S. Pat. No. 5,121,913 discloses an in-mold labeling apparatus and method. The apparatus includes a label transfer assembly having a pair of label carriages, each with two label heads and two suction cups for engagement with labels from a magazine or a source of labels and placement of the labels in mold cavities of a blow molding machine. A continuously rotating drive member operates a first rotary drive to raise and lower the label transfer assembly between the label pick up and label discharge positions while dwelling the assembly at the two positions during fo label pick up and transfer. The drive member also operates a second rotary drive to extend and retract the dwelled label transfer heads at the two positions to pick up labels and then place the labels in mold cavities.
In the in-mold labeling apparatus of U.S. Pat. No. 5,121,913, the loading forces are reduced by providing separate drives connected to a rotating wheel for independently moving the label transfer assembly up and down and independently extending and retracting the label transfer heads. Separate drives reduce transmitted forces and wear. Further, the maximum forces transmitted through the drives are timed to occur at different intervals during the cycle of operation thereby spreading the forces in time and reducing stress on the drive system. The use of a separate drive for extending and retracting label transfer heads reduces the amount of mass moved during this operation with a commensurate reduction in forces experienced along the drive train.
U.S. Pat. No. 5,104,306 discloses an in-mold labeling system. A division of the application which issued as that patent itself issued as U.S. Pat. No. 5,256,365 and discloses a related in-molding labeling method. The system includes an in-mold labeling apparatus for moving labels to a rotary blow-molding machine and placing the labels in the cavities of mold sections and a rotary label transfer apparatus for withdrawing labels from label magazines and presenting the labels for pick up by the transfer heads of the in-mold labeling apparatus. The in-mold labeling apparatus includes pairs of label transfer heads on each side of the apparatus. Separate rotary label transfer apparatus are provided on each side of the in-mold labeling apparatus to present labels to the adjacent label transfer heads. Each rotary transfer apparatus includes a pair of rotary transfer wheels and a pair of label magazines, one magazine for each wheel. The wheels carry transfer units which are moved to positions opposite the magazines, are extended to engage labels in the magazines, are withdrawn, and are moved to pick up positions where the labels are transferred to the transfer heads of the in-mold labeling apparatus. During movement to the pick up positions, the labels may be rotated to assure proper angular orientation when picked up by the in-mold labeling apparatus for placement in the mold sections.
The rotary transfer wheels operate to pick up labels from the magazines and move the labels for pick up by the in-mold labeling apparatus during the relatively long time interval while the in-mold labeling apparatus transfer heads move the labels to the mold sections, place the labels in the mold cavities, and return to pick up the next labels. This long cycle period provides sufficient time to form reliable vacuum connections between the vacuum cups on the heads of the transfer wheels and the lead label in the label magazine. A sufficiently high vacuum is used to assure a connection which withdraws one label at a time from the magazine. The pressure in the suction cups holding the labels on the transfer wheels is reduced before the labels are moved for pick up by the in-mold labeling apparatus in order to facilitate ready transfer of the labels held by the suction cups of the wheel to the suction cups of the in-mold labeling apparatus transfer heads.
Reliable label pick up from the magazines is facilitated by movement of the label transfer heads in the units directly toward the magazines so that the suction cups do not move laterally with respect to the magazines during engagement with the lead labels and during withdrawal of the captured individual labels from the magazines. The rotary label transfer apparatus includes a pair of rotary wheels that pick labels from magazines and move the labels to positions for pick up by the transfer heads. Location of the label magazines in free available space within the in-mold labeling system is facilitated by use of a first, large-diameter rotary wheel having three 120 degree-spaced label transfer units and a second, relatively smaller diameter wheel having four 90 degree-spaced label transfer units. Both wheels are rotated in steps with the first wheel rotated 120 degrees in each step and the second wheel rotated 90 degrees in each step. Each wheel simultaneously supplies labels to the in-mold labeling apparatus while permitting the two label magazines to be oriented at different angles in desired locations within the in-mold labeling system.
To overcome the shortcomings of conventional blow-molding machines having in-mold labeling (IML) capability, a new machine having a universal in-mold labeling (UIML) capability is provided. In view of the relatively large commercial demand for various types of labeled plastic articles, it would be desirable to have a blow-molding machine that can produce high-quality, labeled articles quickly and at a relatively low cost. The present invention satisfies this desire.
An object of the present invention is to upgrade various components of conventional IML apparatus and also provide increased accuracy in label placement onto the article. Related objects are to improve the efficiency of conventional IML apparatus, increase production, and reduce scrap. Another object is to overcome the relatively low output of conventional apparatus by producing articles with relatively high output.
It is still another object of the present invention to avoid difficult setup procedures. An additional object is to provide a control system that coordinates and controls operation of the various components of the system. Yet another object is to provide increased control over key parameters during the in-mold labeling process.